Radioactive Xe has been injected into Al, A1 2O 3, Ta, Ta 2O 5, Ag, and Au at energies up to 40 keV, and the targets then heated in vacuum to determine the release behavior. On the basis of diffusion calculations, in which release temperatures are correlated with ΔH' s and range parameters, it is shown that the components of release are generally of three types, though there may be occasional effects due to phase changes. Release compatible with conventional diffusion data, i.e. “normal diffusion”, is found under conditions of high bombardment energies, low gas concentrations, and (in some cases) annealing. A process, the temperatures for which lie between the bombardment temperature and that for “normal diffusion”, is prominent whenever the energy is below 1 to 4 keV, the value depending on the target. This process is possibly the result of either bombardment damage (hence the name “damage diffusion”) or the proximity of the surface. Release characterized by high temperatures correlates with high gas concentrations. There is good evidence that it is associated with the formation and motion of bubbles (hence the name “bubble diffusion”). Effects due to phase changes are observed in the particular cases of Al (melting) and Ta (oxide dissolution). Processes resembling those observed here can also be recognized in a variety of published results. Included are studies on bombarded targets under conditions of average cleanliness, on bombarded oxidefree W under conditions of ultra-high vacuum, on surfaces used for ion pumping, and on materials containing fission Xe.